In recent years, as part of efforts against environmental problems, low-pollution cars have been developed, and the cars include a fuel cell vehicle in which a fuel cell stack is used as a car-mounted power source. The fuel cell stack has a stack structure in which a plurality of cells are stacked in series, and each cell has a membrane-electrode assembly in which an anode pole is arranged on one face of an electrolytic film, whereas a cathode pole is arranged on the other face thereof. A fuel gas and an oxidizing gas are supplied to the membrane-electrode assembly to cause an electrochemical reaction, and chemical energy is converted into electric energy. Above all, a solid polymer electrolyte type fuel cell stack in which a solid polymer film is used as an electrolyte can easily be made compact at a low cost, and additionally it has a high output density. In consequence, the use application of the fuel cell stack as the car-mounted power source is expected.
When a fuel cell system is operated, it is necessary to detect a power generation error caused by a deficiency in the supply of the reactant gas due to flooding, the drying of the membrane-electrode assembly or the like, thereby recovering the state of each cell so as to take out a sufficient output. In Japanese Patent Application Laid-Open No. 2004-165058, there is suggested a technology for monitoring the lowering of a cell voltage, and executing cell voltage recovery processing while limiting the output, in a case where the cell voltage is below a predetermined lower limit voltage threshold.
[Patent Document 1] Japanese Patent Application Laid-Open No. 2004-165058